The present invention relates to a rubber-reinforced styrenic polymer exhibiting increased elongation, in particular, to a mixture of a rubber-reinforced styrenic polymer and an aliphatic diester and to a method for preparing the mixture.
Due to their physical and chemical properties, rubber-reinforced polymer resins derived from a monovinylidene aromatic compound such as styrene or a derivative of styrene, and optionally, one or more comonomers, are employed in a variety of commercial applications such as packaging, refrigerator linings, automotive parts, furniture, castings for domestic appliances and toys. In general, the rubber-reinforced polymers comprise discrete particles of rubber, e.g., cross-linked polybutadiene or a block copolymer of butadiene and styrene, dispersed throughout a continuous polymer matrix phase derived from styrene (conventionally referred to as high impact polystyrene or HIPS) or styrene and a comonomer such as acrylonitrile (conventionally referred to as ABS).
The mechanism by which a material fails and the type of failure is known to be dependent on the physical properties of the material. For example, materials possessing high elongations will generally fail in a ductile type manner. Ductile failure is a failure accompanied by deformation prior to break and is conventionally evidenced by a fracture or break without formation of splinters. Alternatively, materials having relatively lower elongation exhibit a brittle type failure which occurs without significant deformation prior to break as commonly as evidenced by the fracture or break being splintered. For this reason, a brittle type failure is less desirable than a ductile fracture in most applications.
In view of these differences in failure mechanisms resulting, to a large extent, from differences in elongation of a material, for many end-use applications it is often desirable to increase the elongation of the material.
The elongation of a material is normally considered to be the elongation at break expressed as a percentage of the original elongation. Elongation of the rubber-reinforced styrenic polymers is conventionally determined using standard tensile property testing techniques which involve pulling a dumb bell shaped sample at its two ends until failure. The speed at which this tensile testing is conducted will have a large influence on the properties, particularly elongation properties, measured. It is important that good elongation be maintained at low pulling speeds such as 5 millimeter (mm) per minute (min) as well as high pulling speeds such as 100 mm/min.
Heretofore, one method for increasing the elongation of a rubber-reinforced styrenic polymer involves modifying the composition of the rubber-reinforced polymer such as by increasing the amount of rubber dispersed as discrete particles throughout the continuous polymer matrix phase. Alternatively, the elongation of the rubber-reinforced polymer can also be increased by increasing the average particle size of the disperse rubber phase and/or otherwise modifying the physical or chemical make-up of the rubber-reinforced polymer. Unfortunately, sufficient elongation can only be achieved using these techniques at the expense of one or more other properties of the rubber-reinforced product.
In view of these deficiencies, it remains highly desirable to provide a rubber-reinforced styrenic polymer which exhibits a relatively high elongation at a variety of pulling speeds which elongation is achieved without significantly and deleteriously affecting the other properties of the rubber-reinforced polymer.